Luminescent tube system and apparatus



March a, 1945. P, OU H ETAL 2,370,635

LUMINESCENT TUBE SYSTEM AND APPARATUS Filed Oct. 21, 1941 yotnZWPatented Mar. 6, 1945 LUMINESCENT TUBE SYSTEM AND APPARATUS CharlesPhilippe Boucher, Paterson, and Frederick August Kuhl, Ridgewood, N. Jassignors to Boucher Inventions, Ltd., a corporation of DelawareApplication October 21, 1941, Serial No. 415,964

11 Claims.

Our invention relates to fluorescent gas discharge tube lighting, andmore specifically concerns a new high voltage fluorescent lightingsystem, together with a new form of high leakage reactance transformerfor energizing the same.

An object of our invention therefore is to produce a new form of highleakage reactance transformer for operating high voltage fluorescentlighting equipment at high efliciency, which is characterized by itscompactness, small size, reliability, simplicity, low first cost, andlow cost of operation.

Another object is to produce an electrical system capable of operatingfluorescent tube lighting at high potentials with steady light emissionhaving only slight flicker. if any, all with a maximum of simplicity andwith the substantial absence of fragile auxiliaries, which system ischaracterized by its high efficiency and low operating costs.

Other objects and advantages will in part be obvious and in part pointedout hereinafter.

Our invention accordingly resides in the several elements and featuresof construction and operational steps, and the relation of each of thesame with one or more of the others, all as described herein, the scopeof the application of which is developed in the accompanying claims,forming part of this specification.

In the attached drawing,

Figure 1 is a front, and

Figure 2 a side elevation of one embodiment of our invention. theelectrical circuits being indicated diagrammatically.

Figure 3 is a view similar to Figure l, but illustrating a secondembodiment of our invention.

To facilitate thorough understanding of our invention, it may be notedat this point that during the past several years, fluorescent tubelighting has come more and more to replace the known incandescentlighting. Such replacement may be attributed to a variety of causes.among some of the more important of which may be included the largenumber of pleasing colors which can be obtained, the pleasing floodlighting effects which can be obtained by the effective use offluorescent tubes, the high efliciency, low operating costs, cooloperation and long life as compared with filamentary bulb lighting. Uponthe solution of several existing technical problems in a manneracceptable to the art, it may safely be assumed that a more completerealization can be obtained of the widespread possibilities of thisstyle of lighting.

Despite its present-day use in the industries,

in commerce, and in household lighting, however, it soon developed thatknown fluorescent tube lighting systems were unduly encumbered by theuse of many fragile, somewhat complicated auxiliaries, including amongthem the familiar iron-core ballast, the starting switch and thestarting compensator. Fixture manufacture was complicated and costly.These constructions, employing hot cathode fluorescent tubes, weresubject to short tube life, unexpected failures of the auxiliaries, andbeing fragile, required careful handling. Additionally, these knownsystems were open to the objection that they could not be operatedsatisfactorily at light intensities lower than those for which the tubeswere rated, and that operation under cold weather conditions wasunsatisfactory.

In our prior applications, Serial No. 402,410 flled July 14, 1941, andSerial No. 402,411, filed July 14, 1941, we disclosed a newautotransformer construction, and a new electrical system embodying thattransformer, which admirably solved many of the problems which hithertohad been considered as somewhat inherent in the art, applicable,however, to those cases when peak voltages of not in excess of about 600volts were impressed across the tubes which were connected in thesecondaries of the new transformers. Long tube life, high operatingeficiencies, sturdiness, compactness, high power factor regulation inthe absence of noticeable tub'e flicker, all were obtained. The tubesfunctioned satisfactorily on dimmer operation, and the arc wouldmaintain under cold weather conditions.

While these autotransformers, because of their simplicity, compactness,low first cost, high -efficiency and low operating costs, are admirablysuited for operation under those low-voltage requirements which areapproved by the Fire Underwriters, practical objecti ns are encounteredin their use for energizing high voltage equipment where the tubesrequire an energizing potential of say 1000 volts or more. Wherevoltages of such values are involved, or in fact, in excess of 600volts, the requirements of the Fire Underwriters are more stringent.Transformers producing such secondary voltages must have completelyinsulated primary coils, i. e., they must be electrically independent ofeach other. The primary winding cannot be grounded. No electricalconnection is permitted between the primary coils and the secondarycoils.

Our present invention is directed to the satisfaction of all of theforegoing requirements. A further object of our invention is, therefore,to

produce a thoroughly practical transformer producing high potential atits secondary terminals, and having high leakage reactancecharacteristics and high efficiency under all operating con ditions forwhich the transformer is designed, which transformer has primary andsecondary coils which are electrically separate from and independent ofeach other, and which are only in inductive association, one with theother. Another object is to produce a high potential fluorescent tubelighting system incorporating such a transformer and being energizedthereby, which system is noteworthy because of its safe operatingcharacteristics under prevailing high voltages, which has highpower-factor and high efliciency, and which gives satisfactoryperformance on dimmer operation, and which will both start rea-dily andmaintain a steady are under cold weather operation, and in whichdetrimental stroboscopic eflect or flicker is reduced to a minimum.

According to our new system, the primary coils may be connected eitherin parallel or series connection, and in either bucking or addingrelationship. Parallel connection possesses the advantage that fullprimary voltage is impressed across each primary coil, so that thesecondary output voltage is practically doubled for given transformationratio. Where series connection of the primary coils across the energysource prevails, however, each: primary coil receives only its share ofthe total potential output of the supply source. For a given operatingvoltage, the number of turns in two parallel connected windings must bedouble the number of turns in two series connected primaries, in orderto maintain a constant volt per turn relationship. We have also found itpreferable to connect the primary coils in opposed or buckingrelationship, such connection resulting in slightly higher efficienciessince when the arc strikes in the load across one secondary coil,assuming that one tube becomes energized before the other, the fiuxshifts from one side of the transformer core to the other, and aidingthe flux already coursing through that side of the transformer core,induces in the corresponding secondary coil a voltage of such magnitudethat any load thereacross, separate and apart from the load across thefirst secondary coil, is immediately energized. Thus with separate orwhat may properly be termed parallel-connected secondary coils, bothtubes constituting the separate loads across the secondaries, eventhough striking separately, are energized within but a few cycles ofcurrent flow, as contrasted with the minimum striking period of 6 to 7seconds in the case of present-day lowvoltage hot cathode systems.

Having reference to the embodiment according to Figs. 1 and 2, this willbe seen to comprise a new transformer according to our invention,together with the associated tube lighting system.

The double circuit parallel magnetic path high potential transformer,possessing high leakage reactance illustratively comprises a central legIII, and outer legs II, I2 extending in spaced parallel relation to saidcentral leg, on opposite sides thereof. These legs extend longitudinallyof the core, and are closed at their ends on each other by end piecesI3. I3 and I4, I4. Mid-core portions MI, M2 serve to interconnect saidouter and central legs near their mid-points, thus dividing thetransformer core into two groups of parallel magnetic paths, of whichthe abutting portion of central leg I!) forms a leg common to each pathin either of the groups. In the first group, one such magnetic path maybe traced from core portion MI to the right along leg II down end pieceI4, across leg I0, and a second parallel path may be traced down thecore portion M2, right along leg I2, and thence up core portion I4 andacross leg I0. Similarly, in the second group, a magnetic path may betraced up core portion MI, to the left along leg II, down end piece I3,across leg I0, and a second parallel path may be traced down the coreportion M2, to the left along leg I2, up core portion I3 and back to M2along leg I0.

The end pieces I3, I3 and I4, I4 and the midcore portions MI, M2 serveto provide pairs of spaces between the central and outer legs, one saidpair of spaces being on each side of the midcore portions MI, M2. Thusthere are a pair of spaces for each group of parallel magnetic paths,the spaces of each pair being on opposite sides of the central leg I0. Aprimary coil and a secondary coil are mounted in said spaces, positionedabout central leg III, with the primary coil adjacent the mid-coreportions MI, M2. These primary and secondary coils are electricallyindependent of each other, and have only inductive association.Intermediate shunts of high leakage reactance extend between eachprimary coil and its associated secondary coil, from legs II and I2respectively, towards but short of central leg I0. Air-gaps comprisingpart of the shunt paths thus are formed, having high reluctancescalibrated in accordance with the loads for which the transformer isdesigned. More specifically, in the first group of parallel magneticpaths, primary coil PI and secondary coil SI are positioned aboutcentral leg III, with primary coil PI adjacent mid-core portions MI, M2.Intermediate shunts ShI, S712 extend between said primary and secondarycoils, which are electrically independent of each other, from outer legsII and I2, respectively. They extend towards but short of central legI0, providing high reluctance air-gaps GI, G2, respectively, calibratedas aforesaid.

In like manner, primary coil P2 and secondary coil S2 are similarlydisposed in the second group of magnetic paths, with the primary coiladjacent mid-core portions MI, M2. shunts Sh3, S714 extend between theprimary and secondary coils, from legs II and I2, respectively. Theyterminate short of central leg Ill, providing airgaps G3, G4, of highleakage reactance calibrated according to the load for which theassociated secondary is designed.

A source of alternating current supply I5, which may constitute theordinary service mains, serves to energize the primary coils PI, P2.While as has been suggested hereinbefore, these primary coils may beconnected in either series or parallel connection and in adding oropposed relation, we here connect them in parallel-opposed relation. Asa result of this connection, the full service potential is impressedacross each secondary coil. Additionally with the primary coils opposedor bucking each other, and assuming parallel secondary connections, eachwith separate load, then when the load increases across one secondarycoil, there is a shift of flux from that magnetic circuit to the other,aiding the primary flux therein, and increasing the voltage induced inits associated secondary coil.

Thus the primary coils are branched across the source I5, and parallelenergizing circuits may be traced as follows: from the right side ofsource I5, through leads I8 and I! to terminal l0, thence to the leftthrough primary coil Pl, terminal I! and leads." and 2|, back to theleft side of source ii. The second circuit may be traced from right sideof source l5, leads l8 and IT, to terminal 22, thence to the rightthrough primary coil P2, terminal 23, and through leads 20 and 2| backto the left side of source I. of course during the next subsequenthalf-cycle of current flow, the direction by which the charging currenttraverses the primary circuits is exactly the reverse of the paths justtraced.

While as has been set forth, either series or parallel (electricallyindependent) secondary circuits can be employed. In this presentdescribed embodiment we employ separate secondary circuits, each circuitbeing electrically independent of the other and each energizing aseparate load.

Because of the inductive nature of the load across the service mainsrepresented by the transformer and system, a lagging current is drawn,reducing the load power factor appreciably. This requires considerableinvestment on the part of a utility company. Equipment of increased wiresizes and larger dimensions are required, and since while the companycharges only for the actual wattage consumed by the user, such companyin reality operates on the basis of current demand. It will be seen thatlow system power factor quickly results in a substantial increase incost to the utility. many industrial and commercial installations. therates assessed by the utilities are dependent upon the power factordrawn by the particular consumer, and additionally, since low powerfactor requires increased investment on the part of the consumer fromthe service connections into his lines, power factor correction is to beresorted to whenever possible.

Accordingly, we employ a power-factor regulating condenser of capacitysufiicient to restore the system power factor to approximately unity,and while the desired power factor correction can be obtained by placingthe condenser at any point in the primary or secondary leads, we findthat by disposing the condenser 'in one parallel secondary circuit, anadditional valuable result is obtained. By so locating the condenser.the circuit in which it is connected draws a leading current, and henceis appreciably out of phase with the neighboring parallel secondarycircuit.

Now, each time that the energizing alternating current rises from zerovalue during one-half cycle of current flow, up to its peak value, andthen falls back again to zero, before duplicating that phenomenon in theopposite direction. the arc across the tube strikes as the voltagereaches its striking potential, and then extinguishes, when the voltagefalls through its extinguishing potential. Thus the arc strikes andextinguishes during each half-cycle, or 120 times per second for60-cycle energizing current.

there is no appreciable change in the light emission, and it remainsrelatively constant.

In the case of the arc discharge tubes, however, there is no heat ortemperature retentivity across the medium of the arc. As soon as theenergizing voltage falls below the extinguishing po- Similarly, andsince in ill tential, therefore, the tube becomes dark, and remains sountil the arc is again struck during the next half-cycle. It is onlytheinertia of the human vision that gives the illusion of persistence ofillumination, and there is sensed by the eye an objectionable flicker,known as stroboscopic effect.

By placing one secondary circuit out of phase with the other, we areenabled to reduce this stobosoopic flicker to a minimum because at suchtimes as the tube in one secondary circuit is dark, the tube in theother circuit will be energized, and vice versa. Substantially constantlight emission results.

Again having reference to Fig. 1, therefore, it will be seen that thetube TI is series-connected directly across secondary coil SI. Tube Tlmay be considered to be a high voltage fluorescent gas discharge tube,containing a suitable filling of inert gas such as argon, neon or thelike, together with a measured small quantity of mercury, and beinginteriorly coated with a suitable light-emitting fluorescent salt. Whilethe gas pressure of conventional hot-cathode tubes may be at about 4 mm.of mercury, requiring an energizing potential of about 14 volts per inchof length, we prefer to operate our tube at a pressure of from about 6to 10 mm. of mercury. The tube may, for example, have a length of say 6feet, a diameter not over 25 millimeters, and require a terminalpotential of about 1000 volts. Tube TI is connected by leads 2B, 21directly across terminals 24, 25 of secondary coil SI.

Similarly, a tube T2 of like characteristics as tube Tl, may beconnected in series with condenser 28, across terminals 29, 30 ofsecondary coil S2, by means of leads 3|, 32.

Condenser 28 is of capacity sufficient to restore the system powerfactor to approximately unity value. The comparatively high voltage ofthe secondary circuit makes it possible to achieve this result whileretaining the size of the condenser within practical limits.

Condenser 28 giving rise to a leading current in secondary coil S2, theback magnetomotive force from secondary coil S2 is out of phase withthat from secondary coil SI, assuming the loads across each said coil tobe energized. By consequence, the primary flux from coil P2 is notweakened to the same extent as is that from primary coil Pl.Accordingly, since not so much primary flux is required, primary coil P2can be wound of smaller diameter wire than otherwise would be the case,accomplishing a saving both in initial investment and in dimensions ofthe transformer.

Additionally, since the condenser causes increase in voltage in thecorresponding secondary coil S2, then to achieve the same open circuitvoltage across both secondary circuits, we wind the secondary coil S2 ofa few less turns of wire than we do secondary coil S I.

It will be interesting to develop at this point, the manner in whichtheprimary or energizing flux courses the magnetic core, in response toclosure of primary coils Pl, P2 on energy source l5. Because of leadingcurrent required by condenser 28, flux will course first from primarycoil P2, and we will assume that during the halfcycle under discussion.the flux courses in the direction of the arrows to the right of thecoil, along leg l0. There splitting into two streams. one stream of fluxcourses up along core portion Ml, to the left along leg I l, andchoosing the path of minimum reluctance, passes down end piece l3 tocentral leg l0. At the same time, the other stream of flux courses clownmid-core portion M2, to the left along leg 6 2, and choosing the path ofleast reluctance, passes up along end piece I3 to leg ID. The twostreams reuniting at leg I0, course together to the right, along legIll, to primary coil P2. During this passage, the entire body of fluxinterlinks the secondary coil S2, inducing full secondary voltagetherein. During the next subsequent half-cycle, of course, the directionof coursing of flux is reversed, and in such case the flux courses tothe left along central leg II), interlinking secondary coil S2, and thensplits into two streams. One stream courses up along end piece i3, tothe right along leg H, and down core portion Mi, where it joins at legID with the other flux stream and courses back to the primary coil P2.The other stream likewise flows in a direction opposite to the arrows,down end piece I3, to the right along leg I2, up mid-core portion M2, toprimary coil P2.

About 90 to 115 electrical degrees later, flux starts to flow fromprimary coil Pi. Passing to the left during the assumed half-cycle,along I0, it splits into two streams when it meets the body of primaryflux from coil P2. One stream courses up through core portion MI, to theright along leg II, and selecting the path of minimum reluctance,courses down end piece I 4 to central leg Ill. The other stream coursesdown mid-core portion M2, to the right along leg I2, and choosing thepath of least reluctance, courses up end piece I4 to central leg I 0.The two streams of flux there uniting, courses as a single stream, backalong leg I to the primary coil PI. During its passage along leg ID, theflux interlinks secondary coil SI, inducing therein the required highvoltage.

During the next subsequent half-cycle, the direction of coursing of fluxis, of course, just the reverse oi that traced. The path of the flux atsuch times, contra to that shown by the arrows, can be traced just as inthe case of the magnetic circuit embracing primary coil P2 and secondarycoil S2.

Were the primary coils to be connected in aiding rather than bucking,relationship, then the legs I0, I I, I3 would have to be formed oflarger cross-sectional area; and since the mid-core portions MI, M2would be traversed only by out-ofphase flux from the primary coils,their crosssectional area would be appreciably reduced.

Despite the fact that the tubes are conventionally selected of likeelectrical rating, almost invariably it will be found that one parallelsecondary circuit and its associated tube will have an impedanceslightly less than that of the other. In this instance, it mayreasonably be expected that the tube TI, in the inductive side of thetransformer, will be of lesser impedance. Because of its lowerimpedance, the impressed voltage will be sufllcient to strike the arcacross this tube first, the tube being energized in but a fraction of asecond, after the passage of only a comparatively few current cycles.

As soon as this tubestrikes, a counter-magnetomotive force, opposing theprimary flux, is developed by the secondary coil SI. Since the primaryflux seeks the path of least reluctance, and splits in proportion to theadmittance of the several available paths, then with proper design ofintermediate shunts ShI, Sh2 and associated air-gaps GI, G2, only somuch primary flux interlinks secondary coil SI as is required to inducetherein a voltage suflicient to maintain the arc discharge across tubeTI. The remainder of the iii primary flux courses the paths of lesserreluctance. Part will fiow across shunts SM, 8712 and air-gaps GI, G2,but by far the major part of this primary flux makes what we term a fluxhirt. and courses over to the other magnetic path, and join with theflux from primary coil P2. Since the voltage induced in the secondarycoil 82 is a function of the number of turns in the secondary coil andthe quantity and rate of change of the flux coursing through thoseturns, the increased primary flux aids in inducing a voltage of suchelevated value in the secondary coil S2 that the arc across tube T2 isquickly struck.

As soon as both the tubes strike, then steady current flow conditionsmaintain, and the primary flux still follows the path of leastreluctance. Only so much flux courses the several secondary coils as isrequired to induce therein the secondary voltages required to maintainthe arcs across tubes TI and T2.

Assuming the momentary half-cycle to be such as to cause primary flux toflow from the primary coils in the direction of the arrows, flux fromcoil PI flows to the left along leg I 0, splits into two streams andcourses, one stream up mid-core portion MI and to the right along leg II, and the other stream down mid-core portion M2 and to the right alongleg I2. Part of the first stream continues on down end piece II and backto the left along leg I0, interlinking secondary coil SI. By far thegreater part, however, courses down across intermediate shunt Shl andair-gap GI, back to primary coil PI, this path now having the leastreluctance because of the back secondary flux induced by coil SI.Similarly, part of the second stream of flux courses up end piece I4 andback along leg I0 to coil PI, interlinking secondary coil SI during itspassage. The greater part of this primary flux, however, choosing thepath of least reluctance, courses up through shunt Sh2, across air-gapG2, and through leg I0 back to primary coil PI. Thus most of the primaryflux is shunted around secondary coil SI, and only the quantity of fluxinterlinks that coil which is necessary to induce therein the requiredsecondary voltage.

At the same time, the flux from primary coil P2 flows to the right alongleg I 0, and splitting, flows one stream up mid-core portion MI and tothe left along leg II, and the other stream down mid-core portion M2 andto the left along leg I2. Part of the first stream courses down endpiece I3 and back along leg I0 to primary coil P2, interlinkingsecondary coil S2 during its passage. The greater part, however,choosing the path of least reluctance, courses down through shunt Sh3,across air-gap G3 and back to primary coil P2.

Similarly, part of the other stream courses up through end piece I3 tothe right along leg III to primary coil P2, interlinking secondary coilS2, during its passage. The greater part of this stream of primary flux,however, chooses the path which now is of least reluctance, and coursesup through intermediate shunt Shl, across air-gap G4, and back toprimary coil P2. In this manner, the secondary coil is by-passed, andthe greater part of the primary flux is shunted around it. Onlysuflicient flux courses through the secondary coil to induce therein thevoltage required to maintain the arc across tube T2.

A The design of the air-gaps G3 and GI forms an important feature of ourinvention. The condenser 28 gives rise to high impedance in thesecondary circuit including coil 82. Accordingly,

but little flux tends to Interlink this coil. If the shunts SM and SMare not constructed of sumciently high reluctance, therefore, then whenthe tube T2 strikes, the shunts would by-pass such a large proportion ofthe primary flux that the re- I maining primary flux available forinterlinking secondary coil 82 would be insumcient to maintain therequired energizing potentia1 across the tube load, and the arc wouldextinguish. Accordingly, these shunts should include long air-gaps, orwhere desired, the shunts maybe substantially or completely omitted.

To permit understanding of the voltage conditions maintaining in thevarious parts of the systern according to the embodiment underdiscussion, we may say that with a 115' volt source I5, supplying 1.8amperes, primary coil PI is found to draw a current of 1.28 amperes,while primary coil P2 draws 0.92 ampere. Secondary coils SI and S2 areeach found to have a terminal voltage of 900 volts inducedthereacrosawhile the voltage across the terminals of condenser 28 isfound to be 1250 volts.-

The tubes in our new system are found to have better startingcharacteristics, even in cold weather. For example, hot cathode, lowvoltage tubes, the mercury condenses out and operation becomes unstablewhen the surrounding atmosphere falls as low as 52 F., tubes accordingto our invention will operate at stable arc discharge at atmospherictemperatures which are much lower. We ilnd that at low temperatures thesix foot tube draws about 60 milliamperes current, as contrasted with 80milliamperes for operation at about 70 F. at-1000 volts secondarypotential.

In actual practice approximately unity power factor is obtained bybalancing condenser 28 against the lengths of shunts ShIShl. Thesevalues are standardized as the result of experiment, so that asatisfactorily operating transformer results.

In this embodiment, with parallel secondary circuits, wherein thecondenser is connected in one secondary leg, the objectionablestroboscopic flicker is minimized. The capacity of condenser employedcan be used to regulate the tube output. The larger the condenser, thegreater will be the tube output. In other words, system impedancedecreases with increase in condenser capacity.

In the embodiment according to Figure 3, we disclose a series connectionof the transformer secondary circuits. In this embodiment, the severalparallel magnetic paths are symmetrical with respect to each other.While with the use of this series connection both tubes strikesimultaneously, we flnd that for some unknown reason, less voltage thanusual per tube is required to strike the arc across the tubes. Forexample, the arcs will be struck across two tubes, each of fi-footlength, connected across secondaries, each developing 900-volt secondaryvoltage output with 1l5volt supply, at but '72-volts primary input. Evenless primary voltage is required when the condenser is disposed in theprimary circuit.

Somewhat according to the construction illustrated in Figure 1, thetransformer core of the embodiment illustrated in Figure 3 consists of acentral, longitudinally extending leg III, together with outer legs II,I2, extending in parallel, spaced relation to leg I0, one on each sidethereof. End pieces I3, I3 and I4, I4 and midcore portions MI, M2 serveto interconnect said outer and inner legs at their ends and adjacenttheir centers, respectively. The mid-core portions will be seen todivide the transformer core into two groups of parallel magnetic pathsoi which the adjacent portion of central leg III, forms a leg common toeach path in either of the groups. In the first of\these groups, onemagnetic path may be tracedfrom core portion MI, to the right along legI I, down through first end piece I, across leg In, back to MI, and asecond parallel path may be traced from M2, through the outer leg I2, upthrough-end piece I4, across central leg III and back to M2. Similarly,in the second group a magnetic path may be traced up through coreportion MI, to the left along leg II, down through first end piece I3,across the leg I0, back to core portion MI. and a second parallel pathis traced from M2 to the left along le I2, up through core portion I3,and along leg I0 back to core portion M2.

The end pieces and mid coreportions serve to provide a. pair of spacesin each said parallel magnetic path, the spaces of each pair beingprovided on opposed sides of central leg III.

A primary coil PI and a secondary coil SI are disposed about central legIII in the spaces provided in the first parallel path, while a primarycoil P2and a secondary coil S2 are similarly disposed in the spacesprovided in the second paral lel magnetic path. In each instance, theprimary coils are disposed adjacent the mid core portions MI, M2.

Intermediate shunts of high leakage reactance are provided in pairs ineach magnetic path, disposed between the corresponding primary andsecondary coils. These shunts extend from the respective outer legstoward but short of the central leg, thus providing air-gaps of highreluctance calibrated according to the particular load for which thetransformer is designed. Thus, in-- termediate shunts ShI and S712extend between primary and secondary coils PI, SI from outer legs I I,I2 respectively, towards but short of central leg Ill. The air-gaps, Gl,G2 are thus formed between the corresponding intermediate shunts and thecentral leg III. In like manner, shunts Sh3 and SM extend from outerlegs II, I2 respectively, between primary and secondary coils P2, S2,towards but short of. central leg In, providing therebetween highreluctance air-gaps G3, G4, respectively.- The primary and secondarycoils are electrically independent and are solely in inductive relationwith each other.

As has already been developed in connection with the embodimentaccording to Figure 1 the primary coils may be connected either inparallel or in series across source of energy I5, and may be disposed ineither adding relation'on the one hand-or opposed Or'bucking relation,on the other hand; The various advantages attendant upon these severalmodes of connection have alreadybeen discussed in some detail, and neednot be repeated here. Suffice it to say that we prefer to connect theprimary coils in parallel-ropposed relation'across the energy source I5.Thus, a charging circuit for primary coil PI may be traced from-theright-hand side of the source I5 of alternating-current energy supply,through leads I6 and H to terminal I8, thence. to the left throughprimary coil PI, terminal I9, and leads 20, 2I, back to the left-handside of the energy source I5. A corresponding parallel charging circuitfor primary coil P2 may be traced from the right-hand side of source I5,through leads I8 and IT to terminal 22,'thence through the pri mary coilP2. to the right, terminal 23, and through leads 20 and 2| back to theleft-hand side of energy source I5. It will of course be understood thatcurrent flow maintains in the direction described only during theassumed halfcycle of charging current, and that the direction of flowwill be Just the opposite during the next following hali cycIe ofcurrent; flow.

Across the terminals of the secondary coils SI, S2 are provided inseries circuit, fluorescent gas discharge tubes TI, T2, each of whichwill normally be of such length that voltages are required across theirterminals in excess of about 600 volts. For example, the tubesillustrated will normally be about six feet long, requiring about 1000volts each. It will of course be understood that the selection of tubelength is but a matter of routine design, once the fundamental aspectsof our invention are disclosed. The tubes may be of somewhatconventional design, containing a filling or argon, neon or similarsuitable inert gas, together with a small quantity of mercury. The tubesare lined interiorly with a suitable lightemitting fluorescent salt, asis typical of such tubes. A condenser 28 is a likewise provided in theseries-connected secondary circuit of capacity suflicient to correct thesystem power-factor to approximately unity value.

A second secondary circuit can be traced from right-hand terminal 25 ofsecondary coil SI, through conductor 21 to tube TI, across lead 33 totube T2, thence through lead 3| to condenser 28, through lead 3| toterminal 29, thence to the right through secondary coil S2, terminal 30,lead 34, terminal 24, and back to the right through secondary coil SI.The location of condenser 28, of capacity suiiicient to correct thesystem power factor, in series circuit results in its having noinfluence on the phase relations between the primary and secondarycoils. Thus it exercises no efiect on any tube flicker which may occur.The loads across the second secondary coils being substantially equal inthe present embodiment, both primary coils and both secondary coils areof like characteristics, as are the shunts ShISh4 and the air-gapsGI-G'4.

In the embodiment under discussion it makes no particular differencewhether the primary coils are connected in aiding or opposedrelationship, inasmuch as there is no opportunity for flux shift tooccur. Sinceboth tubes have to strike before the secondary circuit canbecome energized, and since the secondary circuit becomes energized as aunit, back magnetomotive forces are created simultaneously in therespective secondary coils, so that a low reluctance path interlinkingthe energized secondary coil, a condition necessary for flux shift, isnot present in the embodiment undergoing discussion.

For an assumed half-cycle of current flow in which the primary magneticflux flows initially substantially in the direction of the arrows, andas illustrative of the conditions before the arc is struck across theseries-connected tubes as shown, let us consider the case of the primarycoil PI. Primary flux generated therein may be assumed to flow to theleft along leg It). When it reaches the region of the common leg of thesecond parallel path previously referred to, the stream of flux hereencounters and opposes (in the described embodiment, wherein the primarycoils are connected in bucking relationship) the flux from the primarycoil P2, which is now in phase with the body of flux from primary coilPI. Splitting into two streams which are of substantially equal value,because of the symmetrical construction of the transformer core andwindings, one stream courses upwardly through core portion MI, to theright along leg II, and choosing the path of least reluctance, coursesdown end piece I4 to common leg I0. At the same time, the other streamcourses through core portion M2 and to the right along leg I2. Likewisechoosing the path of least reluctance, the stream of flux courses up endpiece I4 to central leg Ill. The two streams of flux reuniting in legIII at the right of the secondary coil SI, the combined streams coursethrough the deenergized coil along leg I0, back to primary coil PI.

At the same time, the primary flux from coil P2 passes to the rightalong leg I0 and splitting into two streams at the common magnetic legcomprised of core portion MI, M2 and the adjacent portion of central legI0, one stream flows up core portion MI, to the left along leg II, and

choosing the path of least reluctance coursesdown end piece I3 tocentral leg Ill. The other stream simultaneously courses down coreportion M2, to the left along leg I2, and likewise choosing the path ofleast reluctance, courses up along end piece I3 to central leg I I). Thetwo streams of flux reuniting at leg ID at the left of secondary coilS2, the combined stream now courses along leg III to the right, back toprimary coil P2. During such passage, the fiux interlinks thedeenergized secondary coil S2. At these times a high voltage is inducedin the respective secondary coils SI, S2, which is additive in nature.Of course, during the alternate halfcycles of the current flow, thedirection of coursing of magnetic flux is exactly the reverse in eachparallel magnetic path, of that described.

It may be noted here that were the primary coils to be connected inaiding relationship, the main flux path would be along outer legs I Iand I2, with the combined flux streams flowing through central leg Hi.There would be in effect only a single magnetic path, and the coreportions Ml, M2, since they would be required to accommodate only thatflux of one magnetic circuit which is out of phase with the flux in theother magnetic circuit, could be greatly minimized in cross sectionalarea, or even, for all practical purposes, entirely eliminated.

After the passage of but a few cycles of the charging current, thevoltage impressed across the outerm3st terminals 35, 36 of the tubes Tl,T2, representing the summation of the potentials induced in thesecondary coils SI, S2, excites the two tubes to such an extent that thearc strikes across each tube, in a matter of but a fraction of a secondafter closure of the primary coils on the service mains.

A conductive circuit is now completed through the secondary coils andthe tubes and condenser in series connection therewith. Backmagnetomotive force is immediately developed in each secondary coil,resulting in a secondary flux which opposes the flow of primary fluxthrough the particular magnetic circuit interlinking the secondarycoils. The primary flux, seeking the paths of least reluctance, nowby-passes in large measure the metallic circuits interlinking thesecondary coils, and by far the larger part of the primary flux coursesthrough the high re luctance intermediate shunts SH! and SH2 andassociated air-gaps GI and G2, on the one hand, and the high reluctanceintermediate shunts SH3 and SH4 and the associated air-gaps G3, G4, onthe other hand. The reluctance of these intermediate shunts iscalibrated to values whereby, with the exception of Just sufllcient fluxto induce in the secondary coils a potential sufficient to maintain thearc discharge across the tubes in the secondary circuits, they by-passall the primary flux around the secondary coils. Since the condenser 28has no effect on the phase relationship of the tubes Tl, T2, because ofits connection in a single series-connected secondary circuit, and sinceit is desirable that the secondary coils SI, S2 divide the secondaryload equally therebetween, we design the primary coils Pl, P2 of thesame electrical characteristics, and treat similarly the secondary coilsSI, S2. Because of this symmetrical construction and connection, shuntsSKI-8H4 are all of the same reluctance as are the air-gaps Gl-Gd.

As has already been suggested, the series-connection of the tubes asdescribed possesses the advantage that for some unknown reason, lessvoltage per tube is required to strike the arc thereacross. Thus, in theexample under discussion, wherein the induced potential at the terminalsof each secondary coil is about 1000 volts for 115 volt primary input,we find that 72 volts impressed, across the primary coils is suflicientto cause two series-connected tubes, each six feet long, to strike withcertainty, even less striking voltage across each tube is required wherethe power-factor correction condenser is disposed in the primarycircuit.

Just as in the case of the parallel-connected or separate secondaries,the condenser may be employed in the series connected secondary toregulate the tube output. The difierences exist, however, that where inthe parallel connection a larger condenser is employed to ensure highertube output, in the present arrangement herein we employ a smallercondenser to accomplish that end. Where in the parallel connection thesystem impedance decreases with increase in the size of the condenserdisposed in one branch, here .where the condenser is disposed in thecomplete secondary circuit, the system impedance increases with increasein the capacity of the condenser.

Our new invention, of which two preferred embodiments have beendescribed for purely illustrative purposes, and in which the primary andsecondary coils are electrically independent of each other, permits theuse of a high leakage reactance transformer with comparatively highvoltage fluorescent gas discharge tubes. Thus, the advantages attendantupon the elimination of the use of fragile and complicated auxiliaryequipment can be obtained even in those cases where the requiredvoltages are such that the Fire Underwriters prohibit the use ofautotransformers. Both costs of fixtures and the cost of installing theauxiliary equipment in such fixtures are considerably reduced ascompared with known hot cathode equipment.

The system is absolutely safe from the standpoint of electricalinstallation, and gives rise to high system power-factor, with at leastin one embodiment, the reduction to a minimum of detrimentalstroboscopic efiect. High efliciency of both the system and thetransformer are obtained with the life expectancy of both tube andtransformer brought to optimum values. In the first describedembodiment, upon striking the arc across the tube load in one parallelsecondary circuit, the construction of the transformer is such that theflux in the one parallel branch thereof shifts, and aids in theproduction of a momentarily increased voltage in the second parallelcircuit, ensuring rapid energization of the tube load therein.

We claim: 1

1. A high leakage reactance transformer comprising a longitudinallyextending central le outer legs disposed in spaced parallel relation tosaid central leg; end pieces and mid core portions interconnecting saidouter and central legs at their ends and adjacent their centers,respectively; pairs of intermediate high leakage reactance shunts, eachincluding an air-gap of high reluctance calibrated in accordance withthe particular load for which the transformer is designed, disposed oneach side of said mid core portions and extending from respective outerlegs towards but short of said central legs; a primary coil and asecondary coil disposed around said central leg on each side of said midcore portions, with each primary coil disposed adjacent said mid coreportions and with each pair of intermediate shunts separating thecorresponding primary and secondary coils, the intermediate shuntsby-passing the primary flux around the corresponding secondary coil uponincrease of the load energized by said coil, and the air-gaps in a firstpair of intermediate shunts being of greater reluctance than theair-gaps in the second pair, to accommodate a secondary load of greatercapacitative reactance.

2. A high leakage reactance transformer comprising a longitudinallyextending central leg; outer legs dis-posed in spaced parallel relationto said central leg; end pieces and mid core portions interconnectingsaid outer and central legs at their ends and adjacent their centers,respectively; pairs of intermediate high leakage reactance shunts, eachincluding an air-gap of high reluctance calibrated in accordance withthe particular load for which the transformer is designed, disposed oneach side of said mid core portions and extending from respective outerlegs towards but short of said central leg; a primary coil and asecondary coil disposed around said central leg on each side of said midcore portions, with each primary coil disposed adjacent said mid coreportions and with each pair of intermediate shunts separating thecorresponding primary and secondary coils, the intermediate shuntsby-passing the primary flux around the corresponding secondary coil uponincrease of the load energized by said coil, and the airgaps in a firstpair of intermediate shunts being of greater reluctance than theair-gaps in the second pair, to accommodate a secondary load of greatercapacitative reactance, the corresponding secondary coil being wound ofa slightly fewer number of turns, while the corresponding primary coilis wound of smaller diameter wire than are the primary and secondarycoils, respectively, in the second magnetic circuit.

3. A fluorescent tube lighting system, comprising a high leakagereactance transformer having a primary winding and two secondarywindings mounted on a core with the secondary windings independent ofthe primary winding, a fluorescent gas discharge tube connected incircuit with the first of said secondary windings, another fluorescentgas discharge tube connected in circuit with the second of saidsecondary windings, shunt core means between the primary winding andsaid first secondary winding to limit the current therein, shunt coremeans of higher reluctance than the previous shunt core means betweenthe primary winding and said second secondary winding to limit thecurrent therein the core, one linking each of said parallel mag- V neticpaths, a fluorescent gas discharge tube connected in circuit with one ofsaid secondary windings, a second fluorescent gas discharge tubeconnected in circuit with the other of said secondary windings, coremeans shunting on only of said parallel magnetic paths at a pointmagnetically between the primary winding and one of said secondarywindings to limit the current in said winding, with the othersecondary'wind' ing positioned closely adjacent the primary winding andwith no magnetic core shunt therebetween, and a condenser in circuitwith said other of said secondary windings and the tube connectedthereto to limit the current in that winding to substantially that ofthe first mentioned secondary winding.

5. A fluorescent tube lighting system, comprising a high leakagereactance transformer in- 'cluding parallel magnetic paths having a legin common, each said magnetic path having therein high leakage reactanceshunts including airgaps, and interlinking primary and secondary coilselectrically independent of each other, disposed, one coil on each sideof said magnetic shunts, with the primary coils disposed adjacent and onopposite sides of said common leg, the electrical circuit of eachsecondary coil being independent of the other; a source ofalternating-current electrical supply across which said primary coilsare connected; a like fluorescent gas discharge tube in each secondarycircuit; and a power-factor regulating condenser disposed in onesecondary circuit and producing a phaseunbalance and limitation ofcurrent flow, the air-gaps in the path which energizes the secondarycoil having the condenser in circuit therewith being of higherreluctance than the air-gaps in the other parallel path.

6. In combination a high leakage reactance transformer including a coreproviding parallel magnetic paths, high leakage reactance shuntsdisposed in each said magnetic path, and primary and secondary windingsmounted on the core with a primary coil and an electrically independentsecondary coil interlinking said magnetic path, one coil being disposedon each side of the magnetic shunt with the reluctance of one shuntsubstantially exceeding that of the other; a source ofalternating-current electrical energy across which said primary coilsare connected; and a condenser connected in series with the secondarycoil with which the shunt of higher reluctance is associated to limitthe current in said winding to substantially the same value as that hadin the other secondary winding by reason or the magnetic shuntassociated therewith.

'7. A high leakage reactance transformer including, in combination, aprimary winding and two secondary windings mounted on a core with thesecondary windings independent of the primary winding and of each other,shunt core means between primary winding and one of said secondsecondary windings, shunt core means of higher reluctance than theprevious shunt core means between the primary winding and a secondsecondary winding.

8. In combination, a core providing parallel magnetic paths, highleakage reactance shunts disposed in each said magnetic path, primaryand secondary coils mounted on the core with a primary coil and anelectrically independent secondary coil interlinking each magnetic path,one coil being disposed on each side of the magnetic shunt with thereluctance of one shunt substantially exceeding that of the other, and acondenser connected in series with said secondary coil associated withthe magnetic shunt of greatest reluctance to limit the current therein.

9. In combination, a primary winding and two secondary windings mountedon a core with the secondary windings independent of the primary windingand of each other, shunt core means between primary winding and one ofsaid second secondary windings, shunt core means of higher reluctancethan the previous shunt core means between the primary winding and asecond secondary winding and a condenser connected in series with saidsecond winding to limit the current therein.

10. In combination, a primary winding and two secondary windingselectrically independent of each other mounted on a common core, shuntcore means magnetically between the primary winding and one only of saidsecondary windings to limit the current therein, with the othersecondary winding positioned closely adjacent the primary winding andwith no magnetic core shunt therebetween, and a condenser of suchcapacity connected to said other secondary winding as to limit thecurrent therein to substantially the same value.

11. In combination, a core having two parallel magnetic paths with a legin common, a primary winding mounted on the core and linking both ofsaid parallel magnetic paths, two electrically independent secondarywindings also mounted on the core, one linking each of said parallelmagnetic paths, core means shunting one only of said parallel magneticpaths at a point magnetically between the primary winding and one ofsaid secondary windings to limit the current in that secondary winding,with the other secondary winding positioned closely adjacent the primarywinding and with no magnetic core shunt therebetween, and a condenser ofsuch capacity .connected to: said other secondary winding as to limitthe current in that winding to substantially the same value.

CHARLES PHILIPPE BOUCHER. FREDERICK AUGUST KUHL.

